microblaze: cache: introduce cpuinfo structure

Introduce a minimal cpuinfo structure to hold cache related info. The
instruction/data cache size and cache line size are initialized early in
the boot to default Kconfig values. They will be overwritten with data
from PVR/dtb if the microblaze UCLASS_CPU driver is enabled.

The cpuinfo struct was placed in global_data to allow the microblaze
UCLASS_CPU driver to also run before relocation (initialized global data
should be read-only before relocation).

gd_cpuinfo() helper macro was added to avoid volatile
"-Wdiscarded-qualifiers" warnings when using the pointer directly.

Signed-off-by: Ovidiu Panait <ovpanait@gmail.com>
Link: https://lore.kernel.org/r/20220531181435.3473549-10-ovpanait@gmail.com
Signed-off-by: Michal Simek <michal.simek@amd.com> (s/bralid/brlid/)